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Best Coax?
- Thread starter 717seemore99
- Start date
Hey QRN
I like your saying...
Light travels faster than the speed of sound, this is why some people tend to appear bright, until they decide to speak
I like your saying...
Light travels faster than the speed of sound, this is why some people tend to appear bright, until they decide to speak
You and I have agreed on a lot of things in the past but on this one we disagree. It's simple math really,just compute the circumferance of a piece of #14 solid wire and then compute the total circumferance of the 7 strands of #19 (?) gauge wire that make up a piece of #14 stranded wire and see which has the greater surface area.I don't have my copper wire chart handy and it's too late for me to think about it right now so I'l let you do the math.
The Heliax is the best thing to use if one has to go 160~ ft to get to the antenna. Wow, that's quite a distance, but it still loses some - about .4 of a Db on that long of a run. So that works out to 8-10% power loss from the radio to antenna over that length. But if the antenna is 100+ ft off of the ground; then the Db gain created by height and the use of a high-efficienct antenna - is still going to get out like mad!
That stuff is frightfully expensive, and for that much of it must cost hundreds of dollars. It's thick - 1 5/8" across - and must be supported along the entire length of the tower. Cell phone companies use the stuff and occasionally dump it and replace it with new cable. (It sure would be fortunate to get some of this older cable for pennies on the dollar!)
Using the 123/*freq in Mhz* x *velocity factor* for the 1/8 wave baseline figure, then multiply that number by odd numbers (1, 3, 5, 7, etc); then one can figure out the optimal usable lengths that resonates the coax and furthers the efficiency of the coax length being used.
If the Heliax is using ultra-low oxygen content copper and it is hollow; then they have maximized the efficiency - but at a very high cost. But with a huge run; it becomes a necessity if one want to minimize loss and get maximum transmission strength. For any run under a 100 ft, using Belden 9913 Flex or Times LMR-400 Flex would be both cost efficient and allow for acceptable low Db loss. For a CB/10 meter export radio with an antenna base thirty feet off of the ground to the radio (about 50~ ft after it takes a few turns to get to your radio), I would take the Belden or Times cable, and pocket the rest of the money!!!!!
That stuff is frightfully expensive, and for that much of it must cost hundreds of dollars. It's thick - 1 5/8" across - and must be supported along the entire length of the tower. Cell phone companies use the stuff and occasionally dump it and replace it with new cable. (It sure would be fortunate to get some of this older cable for pennies on the dollar!)
Using the 123/*freq in Mhz* x *velocity factor* for the 1/8 wave baseline figure, then multiply that number by odd numbers (1, 3, 5, 7, etc); then one can figure out the optimal usable lengths that resonates the coax and furthers the efficiency of the coax length being used.
If the Heliax is using ultra-low oxygen content copper and it is hollow; then they have maximized the efficiency - but at a very high cost. But with a huge run; it becomes a necessity if one want to minimize loss and get maximum transmission strength. For any run under a 100 ft, using Belden 9913 Flex or Times LMR-400 Flex would be both cost efficient and allow for acceptable low Db loss. For a CB/10 meter export radio with an antenna base thirty feet off of the ground to the radio (about 50~ ft after it takes a few turns to get to your radio), I would take the Belden or Times cable, and pocket the rest of the money!!!!!
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Yes, I did just pass.
Thank You Very Much!
At that height, there is little *impediment of propagation* and ALL of the Db gain of that 'efficient antenna' would be realized.
Is that better?
I'm not writing a dissertaion, just thinking out loud.
Can you tell the difference?
BTW - I NEVER said that I had ALL of my ducks in a row about radio or RF engineering - neither does any General for that matter.
Didn't you say, that you are an RF engineer?
Oh, you're an antenna tech...
"....The feedline must be in odd multiple lengths of 1/8-wavelength on the lowest operating frequency to optimize the impedance presented to the balun over the frequency range of the antenna. This length can be calculated using the following formula, or use Table 1.
The DX Engineering 300 Ω ladder feedline has a VF of 0.88.
Formula:
123 / Freq (MHz) x VF: Multiply the result times the ODD multiple (1, 3, 5, 7, etc.) to get the correct length that is closest to your required feedline length.
Where:
123 = 1/8-Wavelength Factor
Freq = Frequency in MHz
VF = Velocity Factor of Feedline..."
There's some clarification. I was just reading this before I wrote what I did. I'm getting the factors together to put up my dipole.
http://www.dxengineering.com/pdf/Multi-Band Dipoles.pdf
The DX Engineering 300 Ω ladder feedline has a VF of 0.88.
Formula:
123 / Freq (MHz) x VF: Multiply the result times the ODD multiple (1, 3, 5, 7, etc.) to get the correct length that is closest to your required feedline length.
Where:
123 = 1/8-Wavelength Factor
Freq = Frequency in MHz
VF = Velocity Factor of Feedline..."
There's some clarification. I was just reading this before I wrote what I did. I'm getting the factors together to put up my dipole.
http://www.dxengineering.com/pdf/Multi-Band Dipoles.pdf
It need not be that large at all. The Heliax commonly refered to as "inch and five eights" is really 1.98 inches and is used in commercial applications for either high power or really low loss at UHF freqs. I have used 1 5/8 Heliax in FM broadcast applications as well as the larger stuff. Commonly used Heliax in communications is 1/2 inch which is only 0.63 inches overall diameter. I have several runs of it on my tower. Loss at 30 MHz is only 0.369 dB/100 ft.
Sounds like a piece of made up physics to me.Actually I saw that in your link to the DX Engineering site. Do NOT believe that and follow it as a rule. It is just a piece of info that DX Engineering has come up with in order to make their antenna work on several bands by presenting an impedance that the balun can handle.Any antenna can be made to work if you play with the feedline lengths.Only in rare instances should that ever be required however.
Having used several 'multi-band' antennas I can say that in a few instances feed line length can make them work 'better'. After going through all the trouble of finding those 'sweet spots', I also found that finding those 'sweet spots' wasn't all that it was supposed to be performance wise. That's not 'definitive' by any means, just what I found that I can 'put up' with. (That's with ladder line, not coax, which is an entirely different animal.)
I've also found that 'DX Engineering' isn't always right about things, at least not in my experience. But then I've found very few people who agree with me completely, so big deal, right?
- 'Doc
I've also found that 'DX Engineering' isn't always right about things, at least not in my experience. But then I've found very few people who agree with me completely, so big deal, right?
- 'Doc
I have a very technical question and I hope someone can help me out. I live in a valley basicly surrounded by hills. Right behind my house is a hill and I'm planning on putting my antenna on the top of the hill. My problem is that it's going to take about 1,000-1,200 feet of coax to get from my house to the top of the hill. But once at the top of the hill my antenna will be on the highest ridge around the area. My question is what type of coax or cable should I run? Any advise would be appreciated. Thanks
- 79z-28
- 79z-28